A car seat is typically provided with a headrest on the top end of the seatback for supporting the head of a passenger. In the related art, a variable movement headrest arrangement has been proposed in U.S. patent application Ser. No. 10/184,675 filed on Jun. 28, 2002. The variable movement headrest arrangement can quickly move a support forwards in the case of a car collision (a chain-reaction collision) and supports the head of a passenger such that the head of the passenger can be prevented from quickly leaning backwards, and thereby prevents the passenger from receiving serious neck injuries. As shown in FIG. 1, the variable movement headrest arrangement is configured such that, when the back of a passenger strikes a hit plate 1A, which is rotatably installed in the back of a passenger seat by using a hinge shaft, in response to the impact formed by a car collision (a chain-reaction collision), and when the striking force is stronger than the elastic force of a spring 1B biasing the hit plate forwards, the hit plate is pushed backwards and thereby a headrest 3A connected to the upper end of the hit plate by a rod 2A leans forwards.
When the hit plate 1A is pushed backwards by the impact applied from the back of the passenger, the headrest 3A can be moved forwards to a position at which the headrest can support the head of the passenger. However, when the head of the passenger leans backwards after the back of the passenger has impacted the hit plate and when the contractile force of the extended spring 1B in the above state is stronger than the striking force applied to the hit plate, the hit plate may be quickly returned forwards to its original position and thereby the headrest may be returned backwards to its original position. Therefore, the variable movement headrest arrangement is problematic in that it cannot effectively support the head of the passenger which leans backwards slightly too late when the headrest is being moved backwards or has been moved backwards.